The invention relates to a method for preparing thiol compounds.
In Lamoureux G. L. et al., Pesticide Biochemistry and Physiology 14, pages 50-61 (1980) the in vitro metabolism of pentachloronitrobenzene (PCNB) into pentachloromethylthiobenzene (PCTA) by means of an enzyme system obtained from onions is described. More particularly, this reference relates to the in vitro preparation of PCTA from PCNB at a pH of 7.9 by means of an enzyme system which contains dithiothreitol, glutathione and S-adenosylmethionine. The enzyme system was prepared from onion roots by ammonium sulphate fractionation and differential centrifugation. The enzyme system contained glutathione-S transferase activity with PCNB, C--S-lyase activity (also termed .beta.-lyase activity) with S-(pentachlorophenyl)cysteine, S-adenosylmethioninemethyl transferase activity with pentachlorothiophenol (PCTP), and probably a few other peptidase activities. The yield of the thiol compound concerned, namely pentachlorothiophenol (PCTP) is, however, negligible in this method compared with the yield of PCTA (see page 55, right-hand column, lines 10-13 from bottom) so that this method is considered unsuitable for preparing thiol compounds on a commercial scale.
In Journal of Biological Chemistry, vol. 253, 24, pages 8854-8859 (1978), the cysteine conjugate .beta.-lyase in rat liver is described. This enzyme catalysing cleavage of the thioether linkage in cysteine conjugates has been purified about 500-fold from rat liver cytosol. However, according to the chapter "Assay Methods" (page 8855), the thiol compounds obtained were directly methylated whereafter the methylated derivatives were identified by spectroscopy methods.